Function - MICR Code Reader

Function - MICR Code Reader.cs

using Microsoft.Azure.WebJobs;
using Microsoft.Azure.WebJobs.Extensions.Http;
using Microsoft.Azure.WebJobs.Host;
using System;
using System.Drawing;
using System.IO;
using System.Net;
using System.Net.Http;
using System.Text.RegularExpressions;
using System.Threading.Tasks;
using Tesseract;

namespace MicrCodeReader
{
    /// <summary>
    /// Some resources which have helped for this implementation:
    /// - https://kimsereyblog.blogspot.ca/2016/05/extract-text-from-images-in-f-ocring.html
    /// - https://github.com/charlesw/tesseract
    /// - https://github.com/wealthsimple/cheque-ocr
    /// - https://www.hanselman.com/blog/WhatIsServerlessComputingExploringAzureFunctions.aspx
    /// </summary>
    public static class MicrCodeReader
    {
        private const string LANGUAGE_CODE = "micr";
        private const string MICR_CHARACTERS = "0123456789abcd";
        private const string CANADIAN_CHEQUE_REGEX = @"[0-9]+ca(?<transit>[0-9]{4,5})d(?<institution>[0-9]{3})a(?<account>[dc0-9]+)";

        [FunctionName("MicrCodeReader")]
        public static async Task<HttpResponseMessage> Run([HttpTrigger(AuthorizationLevel.Anonymous, "post", Route = null)]HttpRequestMessage request, TraceWriter log)
        {
            var bitmap = (Bitmap)null;
            var micrNumbers = string.Empty;
            var meanConfidence = float.MinValue;

            using (var imageStream = await request.Content.ReadAsStreamAsync())
            {
                using (var memoryStream = new MemoryStream())
                {
                    imageStream.CopyTo(memoryStream);
                    memoryStream.Position = 0;
                    bitmap = new Bitmap(memoryStream);
                }
            }

            //Used when hosted on Azure Function on Azure, not locally (ex: "d:\home\site\wwwroot\bin").
            TesseractEnviornment.CustomSearchPath = Environment.GetEnvironmentVariable("TesseractEnviornmentCustomSearchPath");
            var dataPath = Environment.GetEnvironmentVariable("TesseractEnviornmentDataPath")/* "d:\home\site\wwwroot" */ ?? @"./tessdata";

            using (var engine = new TesseractEngine(dataPath, LANGUAGE_CODE, EngineMode.Default))
            {
                engine.SetVariable("tessedit_char_whitelist", MICR_CHARACTERS);
                using (var pix = PixConverter.ToPix(bitmap))
                //using (var pix = Pix.LoadFromFile("./sample_cibc.jpg"))//for local or debug scenario.
                {
                    using (var page = engine.Process(pix))
                    {
                        if (page != null)
                        {
                            meanConfidence = page.GetMeanConfidence();
                            var pageText = page.GetText();
                            if (!string.IsNullOrEmpty(pageText))
                            {
                                pageText = pageText.Replace("\n", string.Empty).Replace(" ", string.Empty);
                                var chequeMatches = (new Regex(CANADIAN_CHEQUE_REGEX)).Match(pageText);
                                if (!string.IsNullOrEmpty(chequeMatches.Groups["transit"].Value))
                                {
                                    return request.CreateResponse(HttpStatusCode.OK, new
                                    {
                                        meanConfidence = meanConfidence,
                                        numbers = new
                                        {
                                            transit = removeNonNumericSymbols(chequeMatches.Groups["transit"].Value),
                                            institution = removeNonNumericSymbols(chequeMatches.Groups["institution"].Value),
                                            account = removeNonNumericSymbols(chequeMatches.Groups["account"].Value)
                                        }
                                    });
                                }
                                else
                                {
                                    return request.CreateErrorResponse(HttpStatusCode.InternalServerError, "NO_CHEQUE_NUMBERS_FOUND");
                                }
                            }
                            else
                            {
                                return request.CreateErrorResponse(HttpStatusCode.InternalServerError, "NO_TEXT_BLOCKS_FOUND");
                            }
                        }
                        else
                        {
                            return request.CreateErrorResponse(HttpStatusCode.InternalServerError, "NO_PAGE_ON_IMAGE_FOUND");
                        }
                    }
                }
            }
        }

        private static string removeNonNumericSymbols(string text)
        {
            if (!string.IsNullOrEmpty(text))
                return (new Regex(@"\D")).Replace(text, "");
            else
                return text;
        }
    }
}